Siloxane
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Phthalic Acid from Potassium Hydrogen Phthalate
For shits and giggles, I started working on a synthesis of luminol by playing along with the NurdRage video ( http://www.youtube.com/watch?v=58Ve69s0qD0 .) My lab happens to have a 20-year-old bulk container of potassium hydrogen phthalate just lying
around, so I had a go at extracting the phthalic acid. Twice.
THE WRONG WAY:
10.00 grams of ancient potassium hydrogen phthalate was slowly dissolved in 400 mL of deionized water, 50 mL at a time, at 22 degrees C. 300 mL of
50% HCl was added in 100 mL increments to precipitate phthalic acid. The precipitate (unquantified) was pitifully small.
The precipitate along with the remaining 100 mL of aqueous solution was heated to drive off water, then heated past 300 degrees C to sublimate
phthalic anhydride. The final unquantified yield was less than one gram.
A BETTER WAY:
30.00 grams of potassium hydrogen phthalate was added to 300 mL of deionized water in a 500 mL beaker along with a Teflon-coated stir bar. The beaker
was moderately heated on a hot plate with vigorous stirring until the potassium hydrogen phthalate was completely dissolved (takes a few minutes.)
100 mL of 50% HCl was added to the solution, causing a dramatic and immediate precipitation of presumed phthalic acid. The beaker containing the
solution and precipitate was labeled and placed under a fume hood to settle overnight.
Apparently, less is more when it comes to water. The first attempt, with 10.00 g of potassium hydrogen phthalate, yielded a small amount of
characteristic cotton-candy-like phthalic anhydride crystals after sublimation. The second attempt leaves me a lot more material to work with.
Tomorrow I'll decant the aqueous portion off, dry the precipitate, and weigh before attempting another sublimation of the anhydride.
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Chemistry Alchemist
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HCl cant go past 38% concentration...
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DJF90
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Potassium hydrogen phthalate serves more value than the phthalic acid you're making from it, as its a primary standard for acidometric titration. Can
you not obtain the acid by other methods?
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phlogiston
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A really easy method is to take old PET bottles, and dissolve those in a hot solution of sodium hydroxide in ethyleneglycol (antifreeze). Allow to
cool, mix with water, acidify and presto.
[Edited on 21-10-2011 by phlogiston]
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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Chemistry Alchemist
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would u need pure ethylene glycol, or could you use the stuff used for cars?
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mr.crow
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Quote: Originally posted by phlogiston  | A really easy method is to take old PET bottles, and dissolve those in a hot solution of sodium hydroxide in ethyleneglycol (antifreeze). Allow to
cool, mix with water, acidify and presto.
[Edited on 21-10-2011 by phlogiston] |
That's the wrong isomer of phthalic acid  we want ortho, not para
Double, double toil and trouble; Fire burn, and caldron bubble
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Siloxane
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Chemistry Alchemist - The HCl was 50% v/v, about 18% w/w.
DJF90 - I thought of that, too. The KHP I'm using is basically waste, since it was received 20 years ago. My lab uses a new container of KHP as a
standard, so no harm done.
BETTER WAY PART DEUCE:
After settling overnight, the precipitate was vacuum filtered through a fritted funnel and allowed to dry for 10 minutes under the forced air stream.
After transfer to a beaker, wet yield was 30.25 grams. The impure precipitate was placed in a (malfunctioning) radiant oven for 20 minutes, then
transferred to a desiccator charged with anhydrous calcium sulfate.
I hope that my next sublimation attempt will work better than the first one; I'll give it a shot on Monday while I fix that damn radiant oven. DIY
PID controller = next level shit.
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Chemistry Alchemist
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Yeah i figured that when i done i typed 50% HCl into google... sorry for not correcting myself
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